Apparatus and method for plasma processing

ABSTRACT

A plasma processing system including a process chamber, a substrate holder provided within the process chamber, and a gas injection system configured to supply a first gas and a second gas to the process chamber. The system includes a controller that controls the gas injection system to continuously flow a first gas flow to the process chamber and to pulse a second gas flow to the process chamber at a first time. The controller pulses a RF power to the substrate holder at a second time. A method of operating a plasma processing system is provided that includes adjusting a background pressure in a process chamber, where the background pressure is established by flowing a first gas flow using a gas injection system, and igniting a processing plasma in the process chamber. The method includes pulsing a second gas flow using the gas injection system at a first time, and pulsing a RF power to a substrate holder at a second time.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional application Ser.No. 60/315,369, filed on Aug. 29, 2001, the entire contents of which areherein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to plasma processing and more particularlyto a method for improved plasma processing.

2. Description of Related Art

Typically, during materials processing, plasma is employed to facilitatethe addition and removal of material films when fabricating compositematerial structures. For example, in semiconductor processing, a (dry)plasma etch process is utilized to remove or etch material along finelines or within vias or contacts patterned on a silicon substrate. Theplasma etch process generally involves positioning a semiconductorsubstrate with an overlying patterned, protective layer, for example aphotoresist layer, into a processing chamber. Once the substrate ispositioned within the chamber, an ionizable, dissociative gas mixture isintroduced within the chamber at a pre-specified flow rate, while avacuum pump is throttled to achieve an ambient process pressure.

Thereafter, a plasma is formed when a fraction of the gas speciespresent are ionized by electrons heated via the transfer of radiofrequency (RF) power either inductively or capacitively, or microwavepower using, for example, electron cyclotron resonance (ECR). Moreover,the heated electrons serve to dissociate some species of the ambient gasspecies and create reactant specie(s) suitable for the exposed surfaceetch chemistry. Once the plasma is formed, any exposed surfaces of thesubstrate are etched by the plasma. The process is adjusted to achieveoptimal conditions, including an appropriate concentration of desirablereactant and ion populations to etch various features (e.g., trenches,vias, contacts, etc.) in the exposed regions of the substrate. Suchsubstrate materials where etching is required include silicon dioxide(SiO₂), poly-silicon and silicon nitride.

As the feature size shrinks and the number and complexity of the etchprocess steps used during integrated circuit (IC) fabrication escalate,the ability to control the transport of reactive materials to andeffluent etch products from etch features, in order to achieve theproper chemical balance necessary to attain high etch rates with goodmaterial selectivity, becomes more stringent.

The etch rate in most dry etch applications, for example oxide (SiO₂)etch, includes a physical component and a chemical component. The plasmachemistry creates a population of positively charged (relatively heavy)ions (such as singly charged argon ions) utilized for the physicalcomponent and a population of chemical radicals (such as atomic fluorineF, and CF, CF₂, CF₃ or more generally CF_(x) species in a fluorocarbonplasma) utilized for the chemical component. Moreover, the chemicalreactants (CF_(x)) act as reactants in the surface etch chemistry andthe (heavy) positively charged ions (Ar+) provide energy to catalyze thesurface reactions.

As feature sizes progressively shrink, they do so at a rate greater thana rate at which the oxide (and other film) thicknesses shrink.Therefore, the etch feature aspect ratio (feature depth-to-width) isgreatly increased with shrinking sizes (of order 10:1). As the aspectratio increases, the directionality of chemical reactant and iontransport local to the etch features becomes increasingly important inorder to preserve the anisotropy of the etch feature.

The transport of electrically charged species (such as ions) can beaffected by an electric force and, therefore, it is conventional in theindustry to provide a substrate holder (chuck) with a RF bias to attractand accelerate ions to the substrate surface through the plasma sheathsuch that they arrive moving in a direction substantially normal to thesubstrate surface. However, the transport of neutral, chemicallyreactive species is not amenable to the application of an electric forceto assert their directionality at the substrate surface.

SUMMARY OF THE INVENTION

The present invention provides a plasma processing system and method ofoperation to affect improvements in chemical transport local to anexposed substrate surface in order to improve etch rate, etchselectivity and etch feature side-wall profile particularly in highaspect ratio features. The exposed substrate surface is exposed toeither material etch or deposition steps, the combination of which serveto alter the material composition and/or topography of the exposedsubstrate surface.

The present invention advantageously provides a plasma processing systemincluding a process chamber, a substrate holder provided within theprocess chamber, and a gas injection system configured to supply a firstgas and a second gas to the process chamber. The system further includesa controller configured to control the gas injection system tocontinuously flow a first gas flow to the process chamber and to pulse asecond gas flow to the process chamber at a first time. The controlleris configured to pulse a RF power to the substrate holder at a secondtime.

The present invention further advantageously provides a method ofoperating a plasma processing system. The method includes the steps ofadjusting a background pressure in a process chamber, wherein thebackground pressure is established by flowing a first gas flow using agas injection system, and igniting a processing plasma in the processchamber. The method further includes the steps of pulsing a second gasflow using the gas injection system at a first time, and pulsing a RFpower to a substrate holder at a second time.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will become moreapparent and more readily appreciated from the following detaileddescription of the exemplary embodiments of the invention taken inconjunction with the accompanying drawings, where:

FIG. 1 depicts a schematic view of a plasma processing device accordingto an embodiment of the present invention;

FIG. 2 is a timing diagram for gas injection pulsing and RF bias pulsingaccording to the embodiment of FIG. 1; and

FIG. 3 outlines a procedure for operating the system of FIG. 1 accordingto the embodiment of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In order to improve etch rate, etch selectivity and etch featureside-wall profile particularly in high aspect ratio features, thepresent invention improves a plasma processing system and method ofoperation to affect improvements in chemical transport local to anexposed substrate surface. The exposed substrate surface is exposed toeither material etch or deposition steps, the combination of which serveto alter the material composition and/or topography of the exposedsubstrate surface. One aspect of material etch and deposition ischemical transport, which can be severely limited in high aspect ratiofeatures due to the low densities associated with low pressureprocessing and lack of chemical transport directivity local to substratematerial features. A method is described herein of periodically pulsinga gas flow in conjunction with pulsing the RF power to the substrateholder in order to affect improvements to chemical transport proximatethe substrate.

Pulsing the gas flow leads to an increase of the gas pressure proximatean exposed surface of a substrate, hence, causing a local reduction inthe mean free path, i.e. an increase in the probability for collisionslocal to the substrate surface. Pulsing the RF power to the substrateholder leads to an increase in the potential drop across the sheath fora duration characteristic of the pulse width during which the sheaththickness is enlarged. The subsequent reduction of the mean free path tovalues less than the sheath thickness leads to a significantly greaterprobability during this short period of time for ion-neutral collisions,either charge exchange collisions or simply momentum transfercollisions, which, in turn, create a greater population of energetic,directional neutral species moving in a direction of normal incidence tothe substrate surface. Therefore, the normal flux of mass and momentumis increased at a feature entrance. The plasma processing system and itsmethod of operation according to the present invention is now described.

The present invention generally relates to a plasma processing systemincluding a gas injection system capable of continuously providing afirst process gas through a first array of gas injection orifices andpulsing a second process gas through a second array of gas injectionorifices. The processing system further includes a RF bias applied to asubstrate holder upon which a substrate rests. The substrate is exposedto a plasma process to facilitate an addition (deposition) or a removal(etching) of a material to or from the substrate.

A plasma processing system 1 is shown in FIG. 1 including a plasmaprocessing chamber 10 wherein a gas injection plate 12 of gas injectionsystem 11 is positioned directly opposite a substrate holder 14 to whicha substrate 16 is attached. The gas injection system 11 facilitates acontinuous injection of a first gas flow 20 and a pulsed injection of asecond gas flow 30 into plasma processing chamber 10 through gasinjection plate 12. The continuous flow of the first gas flow 20originates from a first gas supply 26 through a mass flow controller 24via a gas line 22. The pulsed flow of the second gas flow 30 originatesfrom a second gas supply 36 through a pulsed gas injection manifold 34via a gas line 32.

The processing system 1 of FIG. 1 further includes a RF bias originatingfrom oscillator 50 and applied to substrate holder 14 through impedancematch network 52.

An amplifier 54 increases the amplitude of RF bias signal output fromoscillator 50 subject to amplitude modulation via signal 58 output fromwaveform signal generator 56. The amplifier 54 sends the amplified RFbias signal to the impedance match network 52.

With continuing reference to FIG. 1, substrate holder 14 is biased withRF power, wherein an RF signal originating from oscillator 50 is coupledto substrate holder 14 through impedance match network 52 and amplifier54. Signal amplification is subjected to amplitude modulation via inputsignal 58 from a waveform signal generator 56.

The amplifier 54 can be a linear RF amplifier suitable for receiving anoscillator input from oscillator 50 and an amplitude modulation signal58 from waveform signal generator 56. One example of a signal 58 outputfrom waveform signal generator 56 is a pulse waveform. An exemplarysystem including the amplifier 54 and an internal pulse generator is acommercially available linear RF amplifier (Model line LPPA) fromDressler (2501 North Rose Drive, Placentia, Calif. 92670). The aboveamplifier is capable of operating in continuous mode as well as pulsemode with RF powers ranging from 400 to 8000 W at frequencies rangingfrom 10 to 500 MHz. Moreover, the above amplifier can achieve pulsewidths as short as 20 milliseconds.

Impedance match network 52 serves to maximize the transfer of RF powerto plasma in processing chamber 10 by minimizing the reflected power.Match network topologies (e.g. L-type, π-type, T-type, etc.) forachieving this end are known. Match network settings for tuningcapacitors C1 and C2 in, for example, an L-type configuration, arecontrolled via controller 70 during both start and run-time conditions.Preferably, an automatic match network control methodology is employedto maintain optimal match throughout the entirety of the process.However, the response for typical match networks is approximately 150milliseconds. Therefore, it is not expected that a conventional(mechanically tuned) match network can respond optimally to pulse widthsless than approximately 150 milliseconds. In such a case, a conventionalmatch network is designed for run and start set-points based upon thecontinuous flow process gas conditions. If on the other hand, pulsewidths in excess of several hundred milliseconds are employed,conventional match networks are sufficiently fast to respond and providean optimal impedance match even during pulsing periods. Furtherdiscussion is provided below.

Additionally, the processing system 1 of FIG. 1 further includes avacuum pump system 42 through which process gases and effluent gases canbe removed (or evacuated) from plasma processing chamber 10. Vacuum pumpsystem 42 preferably includes a turbo-molecular vacuum pump (TMP)capable of a pumping speed up to 5000 liters per second (and greater)and a gate valve for throttling the chamber pressure. TMPs are usefulfor low pressure processing, typically less than 50 mTorr. At higherpressures, the TMP pumping speed falls off dramatically. For highpressure processing (i.e. greater than 100 mTorr), a mechanical boosterpump and dry roughing pump is recommended.

Furthermore, the plasma processing system 1 further includes acontroller 70 coupled to vacuum pump system 42, impedance match network52, amplifier 54 and waveform signal generator 56. In addition,controller 70 is coupled to mass flow controller 24, first gas supply26, second gas supply 36 and pulsed gas injection manifold 34 for thepurpose of controlling gas injection parameters in the plasma processingsystem 1.

Controller 70 includes a microprocessor, memory, and a digital I/O portcapable of generating control voltages sufficient to communicate andactivate inputs to the gas injection system 11. Moreover, controller 70exchanges information with impedance match network 52, amplifier 54, andwaveform signal generator 56. The controller 70 exchanges status datawith the gas supplies 26 and 36, mass flow controller 24, and pulsed gasinjection manifold 34. In addition, controller 70 sends and receivescontrol signals to and from vacuum pump 55. For example, a gate valvecan be controlled. A program stored in the memory includes a processrecipe with which to activate the valves and the respective gas flowrate when desired. One example of controller 70 is a Model #SBC2486DXPC/104 Embeddable Computer Board commercially available from Micro/sys,Inc., 3730 Park Place, Glendale, Calif. 91020.

During the operation of the plasma processing system 1, process gas isintroduced to the plasma processing chamber 10 via gas injection system11 wherein means are provided for continuously flowing the first gasflow 20 and means are provided for pulsing the second gas flow 30. Firstand second gas flows 20 and 30 originate from gas supplies 26 and 36,respectively. Gas supplies 26 and 36 can include a cabinet housing aplurality of compressed gas cylinders and can include pressureregulators for safe gas handling practice. The continuous flow of firstgas flow 20 is achieved via a gas showerhead configuration that is wellknown to those skilled in the art.

In a preferred embodiment, continuous flow of first gas flow 20 isintroduced to the process chamber 10 through gas injection plate 12. Inan alternate embodiment, continuous flow of gas flow 20 is introduced tothe process chamber 10 through a chamber wall of the process chamber 10.In a preferred embodiment, mass flow controller 24 monitors and controlsthe mass flow rate of the first process gas being supplied by gas supply26. The pulsing of second gas 30 is achieved via pulsed gas injectionmanifold 34. The pulsed gas injection manifold 34 can include one ormore pressure regulators, one or more pulsed gas injection valves and agas distribution manifold. An exemplary pulsed gas injection system isdescribed in greater detail in pending U.S. application 60/272,452,filed on Mar. 2, 2001, which is incorporated herein by reference in itsentirety. In a preferred embodiment, pulsed flow of second gas flow 30is introduced to process chamber 10 through gas injection plate 12.

In alternate embodiments, gas injection plate 12 can be machined from ametal such as aluminum and, for those surfaces in contact with theplasma, can be anodized to form an aluminum oxide protective coating orspray coated with Y₂O₃. Furthermore, the gas inject plate 12 can befabricated from silicon or carbon to act as a scavenging plate, or itcan be fabricated from silicon carbide to promote greater erosionresistance.

Substrate 16 is transferred into and out of plasma processing chamber 10by means well understood to those skilled in the art. Furthermore,substrate 16 is preferably affixed to the substrate holder 14 viaelectrostatic clamp (not shown) and backside gas (not shown) can beprovided for improved thermal conductance between substrate 16 andsubstrate holder 14. Substrate holder 14 can further include heating andcooling means (not shown) in order to facilitate temperature control ofsubstrate 16.

FIG. 2 presents a schematic illustration of a method of operating theembodiment described in FIG. 1. A first time history of a flow rate ofthe first gas flow 20, generally indicated as 110, is shown, wherein theflow rate 112 is maintained constant during the length of the process. Asecond time history of a flow property of the second gas flow 30,generally indicated as 120, is shown, wherein the flow property 122 ispreferably an injection total pressure. The injection total pressure ispulse modulated via pulsed gas injection manifold 34 with a pulseamplitude 122, pulse width 126 and pulse period 124. A ratio of thepulse width 126 to the pulse period 124 can further be referred to asthe pulse duty cycle. In addition, the pulsed flow property 122 can be amass flow rate of the second gas flow 30.

In concert with the first and second time histories, a third timehistory of the RF bias power, generally indicated as 130, is shown,wherein the RF bias power is pulse modulated between a first power level134 and a second power level 132. The RF bias power pulse has a pulsewidth 138 and a pulse period 136. A ratio of the pulse width 138 to thepulse period 136 can be further referred to as the pulse duty cycle. Ina preferred embodiment, the RF power pulse width 138 and pulse period136 are substantially equivalent to the second process gas pulse width122 and pulse period 124, respectively. In an alternate embodiment, theRF power pulse duty cycle is substantially equivalent to the second gasflow pulse duty cycle. In an alternate embodiment, the second gas flowpulse width is substantially different than the RF power pulse width. Inan alternate embodiment, the second gas flow pulse period issubstantially different than the RF power pulse period. In an alternateembodiment, the second gas flow duty cycle is substantially differentthan the RF power pulse duty cycle. In a further alternate embodiment,the RF power pulse waveform is shifted or offset in time 140 relative tothe second gas flow gas pulse waveform.

The flow rate of the first gas flow 20 can range from 100 to 5000 sccm(equivalent argon flow rate). A chamber pressure can range from 1 to1000 mTorr. The injection total pressure of the second gas flow 30 gascan range from 50 to 1000 Torr. The pulse widths can range from 1 to1000 milliseconds with pulse periods ranging from 10 milliseconds to 10seconds.

In a preferred embodiment, a process recipe according to the method ofoperation presented in FIG. 2 is now described. The first gas flow 20includes a gas mixture of Ar/C4F8/O2 with corresponding flow rates400/7/12 sccm. A background pressure in process chamber 10 is set to 20mTorr, for example, by sensing the chamber pressure in the pumping portor at the chamber wall outside of the processing region and adjustingthe vacuum pump system gate valve. The second gas flow 30 is a mixtureof gases Ar/C4F8/O2 with corresponding partial pressures substantiallyequivalent to those of the first gas flow 20. The gas injection totalpressure for the second gas flow 30 is preferably atmospheric pressure(i.e. approximately 760 Torr). And lastly, pulse widths and pulseperiods are substantially equivalent for the second gas flow pulse andthe RF power pulse and are set at 20 milliseconds and 200 milliseconds,respectively.

In the preferred method of operation, process gas pulse widths of 20milliseconds are achieved via gas injection configurations presented inpending U.S. application 60/272,452, and RF power pulse widths of 20milliseconds are achieved via commercially available RF power sources asdescribed above. Also described above, when RF power pulse widths areless than the response time of conventional impedance match networks(i.e. approximately 150 milliseconds), alternative techniques could berequired to achieve an optimal impedance match. Linear RF amplifiers, asdescribed above, are now being equipped with frequency shift tuning and,in particular, they are available for frequencies of 1.6 to 4 MHz(Dressler RF Technology). For frequencies in excess of commerciallyviable options, one requires alternative solutions such as a freerunning oscillator as described in pending U.S. application 60/143,548filed on Jul. 13, 1999, which is incorporated herein by reference in itsentirety.

In FIG. 3, a method of operating the embodiment depicted in FIG. 1 ispresented. A plasma process is initiated in plasma processing system 1at step 500. In step 510, controller 70 initiates a flow rate 112 forthe first gas flow 20 through gas injection system 11 according to astored process recipe. The first gas flow 20 is continuously introducedto process chamber 10 with a constant mass flow rate 112 from the startof the process in step 500 until the end of the process in step 630. Instep 520, controller 70, coupled to vacuum pump system 42, adjusts thebackground pressure in process chamber 10 according to a stored processrecipe.

Once the first process gas flow rate is established and the backgroundpressure is set, a processing plasma is ignited via substrate holder RFpower in step 530 according to a process recipe stored in controller 70.In step 540, controller 70 triggers second gas flow pulse in step 550and RF power pulse in step 580 with or without a phase delay in step570. The second gas flow pulse is ended in step 560 while the RF powerpulse is ended in step 590, and the process pulse is completed in step600.

In step 610, a process endpoint is evaluated per endpoint detectionmethods such as optical emission spectroscopy, impedance match networkcomponent monitoring, etc. If an endpoint is reached, the process comesto an end in step 630. If the process is not complete, a time delaycomparable to the respective pulse periods for the second process gaspulse and the RF power pulse is enforced in step 620. Thereafter, steps540 through 630 are repeated.

Although only certain exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention.

1. A plasma processing system comprising: a process chamber; a substrate holder provided within said process chamber; a gas injection system configured to supply a first gas and a second gas to said process chamber; and a controller configured to control said gas injection system to continuously flow a first gas flow to said process chamber and to pulse a second gas flow to said process chamber at a first time, said controller being configured to pulse a RF power to said substrate holder at a second time, and said controller is configured to provide a pulse width of said second gas flow that is substantially equivalent to a pulse width of said RF power pulse.
 2. The system according to claim 1, wherein a gas injection plate of said gas injection system is substantially parallel to a substrate receiving surface of said substrate holder, and wherein said gas injection plate is configured to introduce at least one of said first gas flow and said second gas flow into said process chamber in a direction substantially normal to said substrate receiving surface of said substrate holder.
 3. The system according to claim 1, wherein said controller is configured to provide a pulse period of said second gas flow that is substantially equivalent to a pulse period of said RF power pulse.
 4. A plasma processing system comprising: a process chamber; a substrate holder provided within said process chamber; a gas injection system configured to supply a first gas and a second gas to said process chamber; and a controller configured to control said gas injection system to continuously flow a first gas flow to said process chamber and to pulse a second gas flow to said process chamber at a first time, said controller being configured to pulse a RF power to said substrate holder at a second time, and said controller is configured to provide a pulse duty cycle of said second gas flow that is substantially equivalent to a pulse duty cycle of said RF power pulse.
 5. The system according to claim 1, wherein said controller is configured to provide that said first time of said pulse of second gas flow is substantially equivalent to said second time of said pulse of RF power.
 6. The system according to claim 1, wherein said controller is configured to provide that said first time of said pulse of second gas flow is offset from said second time of said pulse of RF power.
 7. The system according to claim 1, wherein said controller is configured to adjust a background pressure in said process chamber.
 8. The system according to claim 1, further comprising an oscillator coupled to said substrate holder for providing said RF power, said oscillator producing an RE signal.
 9. The system according to claim 8, further comprising an amplifier coupled to said oscillator.
 10. The system according to claim 9, wherein said amplifier is a linear amplifier.
 11. The system according to claim 9, further comprising an impedance match network connecting said amplifier to said substrate holder.
 12. The system according to claim 11, wherein said controller is connected to and configured to control said amplifier and said impedance match network.
 13. The system according to claim 9, further comprising a waveform generator configured to produce an input signal and coupled to said amplifier, wherein said RF signal is received by said amplifier and wherein said RF signal is subjected to amplitude modulation via said input signal received by said amplifier from said waveform generator.
 14. The system according to claim 13, wherein said input signal is a pulse waveform.
 15. The system according to claim 13, wherein said controller is connected to and configured to control said waveform generator.
 16. The system according to claim 1, said gas injection system comprising a first gas supply connected to a mass flow controller, and a second gas supply connected to a pulsed gas injection manifold.
 17. The system according to claim 16, wherein said pulsed gas injection manifold comprises a pressure regulator, a pulsed gas injection valve, and a gas distribution manifold.
 18. The system according to claim 16, said controller being connected to and configured to control said first gas supply, said mass flow controller, said second gas supply, and said pulsed gas injection manifold.
 19. A plasma processing system comprising: a process chamber; a substrate holder provided within said process chamber; a gas injection system configured to supply a first gas and a second gas to said process chamber; and control means for providing a continuous first gas flow to said process chamber through said gas injection system, pulses of a second gas flow to said process chamber through said gas injection system at a first time, and pulses of a RF power to said substrate holder at a second time, and said control means is configured to provide a pulse width of said second gas flow that is substantially equivalent to a pulse width of said RF power pulse.
 20. The system according to claim 19, wherein a gas injection plate of said gas injection system is substantially parallel to a substrate receiving surface of said substrate holder, and wherein said gas injection plate is configured to introduce at least one of said first gas flow and said second gas flow into said process chamber in a direction substantially normal to said substrate receiving surface of said substrate holder.
 21. The system according to claim 19, wherein said control means is configured to provide a pulse period of said second gas flow that is substantially equivalent to a pulse period of said RF power pulse.
 22. A plasma processing system comprising: a process chamber; a substrate holder provided within said process chamber; a gas injection system configured to supply a first gas and a second gas to said process chamber; and control means for providing a continuous first gas flow to said process chamber through said gas injection system, pulses of a second gas flow to said process chamber through said gas injection system at a first time, and pulses of a RF power to said substrate holder at a second time, and said control means is configured to provide a pulse duty cycle of said second gas flow that is substantially equivalent to a pulse duty cycle of said RF power pulse.
 23. The system according to claim 19, wherein said control means is configured to provide that said first time of said pulse of second gas flow is substantially equivalent to said second time of said pulse of RF power.
 24. The system according to claim 19, wherein said control means is configured to provide that said first time of said pulse of second gas flow is offset from said second time of said pulse of RF power.
 25. The system according to claim 19, wherein said control means is configured to adjust a background pressure in said process chamber.
 26. The system according to claim 19, further comprising an oscillator coupled to said substrate holder for providing said RF power, said oscillator producing an RF signal.
 27. The system according to claim 26, further comprising an amplifier coupled to said oscillator.
 28. The system according to claim 27, wherein said amplifier is a linear amplifier.
 29. The system according to claim 27, further comprising an impedance match network connecting said amplifier to said substrate holder.
 30. The system according to claim 29, wherein said control means is connected to and configured to control said amplifier and said impedance match network.
 31. The system according to claim 27, further comprising a waveform generator configured to produce an input signal and coupled to said amplifier, wherein said RF signal is received by said amplifier and wherein said RF signal is subjected to amplitude modulation via said input signal received by said amplifier from said waveform generator.
 32. The system according to claim 31, wherein said input signal is a pulse waveform.
 33. The system according to claim 31, wherein said control means is connected to and configured to control said waveform generator.
 34. The system according to claim 19, said gas injection system comprising a first gas supply connected to a mass flow controller, and a second gas supply connected to a pulsed gas injection manifold.
 35. The system according to claim 34, wherein said pulsed gas injection manifold comprises a pressure regulator, a pulsed gas injection valve, and a gas distribution manifold.
 36. The system according to claim 34, said control means being connected to and configured to control said first gas supply, said mass flow controller, said second gas supply, and said pulsed gas injection manifold.
 37. A method of operating a plasma processing system, the method comprising the steps of: adjusting a background pressure in a process chamber, wherein the background pressure is established by flowing a first gas flow using a gas injection system; igniting a processing plasma in the process chamber; pulsing a second gas flow using the gas injection system at a first time for a first pulse width; and pulsing a RF power to a substrate holder at a second time for a second pulse width, wherein said first pulse width being substantially equivalent to said second pulse width.
 38. The method according to claim 37, wherein the step of pulsing the second gas flow is performed for a predetermined pulse period.
 39. The method according to claim 37, wherein the step of pulsing the second gas flow is performed to achieve a predetermined pulse duty cycle.
 40. The method according to claim 37, wherein the step of pulsing the RF power is performed for a predetermined pulse period.
 41. The method according to claim 37, wherein the step of pulsing the RF power is performed to achieve a predetermined pulse duty cycle.
 42. The method according to claim 37, wherein the step of pulsing the second gas flow is performed for a first pulse period, and wherein the step of pulsing the RF power is performed for a second pulse period, said first pulse period being substantially equivalent to said second pulse period.
 43. A method of operating a plasma processing system, the method comprising the steps of: adjusting a background pressure in a process chamber, wherein the background pressure is established by flowing a first gas flow using a gas injection system; igniting a processing plasma in the process chamber; pulsing a second gas flow using the gas injection system at a first time for a first pulse duty cycle; and pulsing a RF power to a substrate holder at a second time for a second pulse duty cycle, said first pulse duty cycle being substantially equivalent to said second pulse duty cycle.
 44. The method according to claim 37, wherein the first time of the pulse of second gas flow is substantially equivalent to the second time of the pulse of RE power.
 45. The method according to claim 37, wherein the first time of the pulse of second gas flow is offset from the second time of the pulse of RF power. 